Pollutant emission control sorbents and methods of manufacture and use

ABSTRACT

Sorbents for removal of mercury and other pollutants from gas streams, such as a flue gas stream from coal-fired utility plants, and methods for their manufacture and use are disclosed. Embodiments include brominated sorbent substrate particles having a carbon content of less than about 10%. Other embodiments include one or more oxidatively active halides of a nonoxidative metal dispersed on sorbent substrate particles mixed with activated carbon in an amount up to 30% by weight. Further embodiments include physical blending of a flow modifier into the sorbent composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.12/329,246, filed Dec. 5, 2008, which is a continuation-in-part of U.S.application Ser. No. 11/860,148, filed Sep. 24, 2007, the contents ofwhich are incorporated herein in their entirety.

TECHNICAL FIELD

Embodiments of the invention relate to sorbents for the removal ofpollutants such as mercury from gas streams, methods for manufacturingsorbents and the use of sorbents in pollution control.

BACKGROUND

Emission of pollutants, for example, mercury, from combustion gassources such as coal-fired and oil-fired boilers has become a majorenvironmental concern. Mercury (Hg) is a potent neurotoxin that canaffect human health at very low concentrations. The largest source ofmercury emission in the United States is coal-fired electric powerplants. Coal-fired power plants account for between one-third andone-half of total mercury emissions in the United States. Mercury isfound predominantly in the vapor-phase in coal-fired boiler flue gas.Mercury can also be bound to fly ash in the flue gas.

On Dec. 15, 2003, the Environmental Protection Agency (EPA) proposedstandards for emissions of mercury from coal-fired electric powerplants, under the authority of Sections 111 and 112 of the Clean AirAct. In their first phase, the standards could require a 29% reductionin emissions by 2008 or 2010, depending on the regulatory option chosenby the government. In addition to EPA's regulatory effort, in the UnitedStates Congress, numerous bills recently have been introduced toregulate these emissions. A number of local and state governments havealso passed or are considering passing stringent regulations to reducemercury emissions, especially from power utility plants. Theseregulatory and legislative initiatives to reduce mercury emissionsindicate a need for improvements in mercury emission technology.

There are three basic forms of Hg in the flue gas from a coal-firedelectric utility boiler: elemental Hg (referred to herein by the symbolHg⁰); compounds of oxidized Hg (referred to herein the symbol Hg²⁺); andparticle-bound mercury. Oxidized mercury compounds in the flue gas froma coal-fired electric utility boiler may include mercury chloride(HgCl₂), mercury oxide (HgO), and mercury sulfate (HgSO₄). Oxidizedmercury compounds are sometimes referred to collectively as ionicmercury. This is because, while oxidized mercury compounds may not existas mercuric ions in the boiler flue gas, these compounds are measured asionic mercury by the speciation test method used to measure oxidized Hg.The term speciation is used to denote the relative amounts of thesethree forms of Hg in the flue gas of the boiler. High temperaturesgenerated by combustion in a coal boiler furnace vaporize Hg in thecoal. The resulting gaseous Hg⁰ exiting the furnace combustion zone canundergo subsequent oxidation in the flue gas by several mechanisms. Thepredominant oxidized Hg species in boiler flue gases is believed to beHgCl₂. Other possible oxidized species may include HgO, HgSO₄, andmercuric nitrate monohydrate (Hg(NO₃)₂.H₂O).

Gaseous Hg (both Hg⁰ and Hg²⁺) can be adsorbed by the solid particles inboiler flue gas. Adsorption refers to the phenomenon where a vapormolecule in a gas stream contacts the surface of a solid particle and isheld there by attractive forces between the vapor molecule and thesolid. Solid particles are present in all coal-fired electric utilityboiler flue gas as a result of the ash that is generated duringcombustion of the coal. Ash that exits the furnace with the flue gas iscalled fly ash. Other types of solid particles, called sorbents, may beintroduced into the flue gas stream (e.g., lime, powdered activatedcarbon) for pollutant emission control. Both types of particles mayadsorb gaseous Hg in the boiler flue gas.

Sorbents used to capture mercury and other pollutants in flue gas arecharacterized by their physical and chemical properties. The most commonphysical characterization is surface area. The interior of certainsorbent particles are highly porous. The surface area of sorbents may bedetermined using the Brunauer, Emmett, and Teller (BET) method of N₂adsorption. Surface areas of currently used sorbents range from 5 m²/gfor Ca-based sorbents to over 2000 m²/g for highly porous activatedcarbons. EPA Report, Control of Mercury Emissions From Coal-FiredElectric Utility Boilers, Interim Report, EPA-600/R-01-109, April 2002.For most sorbents, mercury capture often increases with increasingsurface area of the sorbent.

Mercury and other pollutants can be captured and removed from a flue gasstream by injection of a sorbent into the exhaust stream with subsequentcollection in a particulate matter control device such as anelectrostatic precipitator or a fabric filter. Adsorptive capture of Hgfrom flue gas is a complex process that involves many variables. Thesevariables include the temperature and composition of the flue gas, theconcentration and speciation of Hg in the exhaust stream, residencetime, and the physical and chemical characteristics of the sorbent.

Currently, the most commonly used method for mercury emission reductionis the injection of powdered activated carbon (PAC) into the flue streamof coal-fired and oil-fired plants. Coal-fired combustion flue gasstreams are of particular concern because their composition includestrace amounts of acid gases, including SO₂ and SO₃, NO and NO₂, and HCl.These acid gases have been shown to degrade the performance of activatedcarbon. Though powdered activated carbon (PAC) is somewhat effective tocapture oxidized mercury species such as Hg²⁺, PAC is not as effectivefor elemental mercury, which constitutes a major Hg species in flue gas,especially for subbituminous coals and lignite. The use of brominatedpowdered activated carbon (BPAC) is described in U.S. Pat. No.6,953,494. According to U.S. Pat. No. 6,953,494, bromine species wereintroduced in PAC by a gas-phase process with Br₂ or HBr precursor inthe vapor phase, both of which are highly toxic and a potentialenvironmental hazard.

The coal-fired utility industry continues to seek new, cost-effectivesorbents for controlling mercury emissions while also preserving thevalue of fly ash as a raw material for quality conscious applications.Evaluations of powdered activated carbon sorbents have shown consistent,adverse impacts on fly ash, a coal utilization by-product, sufficient torender it unusable in cement applications. These impacts includeelevated residual carbon levels in the fly ash that exceed applicationspecified limits, interference with the performance of air entrainmentadditives (AEA), which are used to improve the freeze-thaw propertiesand workability of cement, and cosmetic discoloration. Efforts are beingmade in the marketplace to minimize these impacts inherent to carbonbased sorbents.

As noted above, alternatives to PAC or Br-PAC sorbents have beenutilized to reduce mercury emissions from coal-fired boilers. Examplesof sorbents that have been used for mercury removal include thosedisclosed in United States Patent Application Publication No.2003/0103882 and in U.S. Pat. No. 6,719,828. In United States PatentApplication Publication No. 2003/0103882, calcium carbonate and kaolinfrom paper mill waste sludge were calcined and used for Hg removal athigh temperatures above 170° C., preferably 500° C. U.S. Pat. No.6,719,828 teaches the preparation of layered sorbents such as clays withmetal sulfide between the clay layers and methods for their preparation.The method used to prepare the layered sorbents is based on an ionexchange process, which limits the selection of substrates to only thosehaving high ion exchange capacity. In addition, ion exchange istime-consuming and involves several wet process steps, whichsignificantly impairs the reproducibility, performance, scalability,equipment requirements, and cost of the sorbent. For example, a sorbentmade in accordance with the teachings of U.S. Pat. No. 6,719,828involves swelling a clay in an acidified solution, introducing a metalsalt solution to exchange metal ions between the layers of the clay,filtering the ion exchanged clay, re-dispersing the clay in solution,sulfidation of the clay by adding another sulfide solution, and finallythe product is filtered and dried. Another shortcoming of the processdisclosed in U.S. Pat. No. 6,719,828 is that the by-products of the ionexchange process, i.e., the waste solutions of metal ions and hydrogensulfide generated from the acidic solution, are an environmentalliability.

There is an ongoing need to provide improved pollution control sorbentsand methods for their manufacture. It would be desirable to providemineral-based sorbents containing bromine on the sorbent substrate thatcan be manufactured easily and inexpensively, do not impair the value offly ash or pose environmental concerns. Furthermore, simple andenvironmentally friendly methods that effectively disperse bromine onreadily available mineral substrates are needed

SUMMARY

Aspects of the invention include compositions, methods of manufacture,and systems and methods for removal of heavy metals and other pollutantsfrom gas streams. In particular, the compositions and systems are usefulfor, but not limited to, the removal of mercury from flue gas streamsgenerated by the combustion of coal. One aspect of the present inventionrelates to a sorbent made by a method comprising dispersing a bromidesalt on a mineral sorbent substrate by impregnating powdered mineralsubstrate particles with a bromide salt solution followed by drying orby spray-drying a mixture slurry of a bromide salt and a mineral sorbentsubstrate. In one embodiment, the method optionally includes reducingthe particle size of the sorbent particles. Another aspect of theinvention pertains to sorbents that include dispersing of a bromide on asorbent that has low surface area, which significantly improvesHg-capture. Yet another aspect of the present invention providessorbents and methods to enhance the properties of concrete by adding flyash that contain injected brominated mineral sorbents.

One or more embodiments pertain to a sorbent comprisingbromine-containing species dispersed on mineral substrate particles, themineral substrate having a total carbon content less than about 10weight percent, the sorbent being adapted for removing mercury from acombustion flue gas in an exhaust gas system. In one or moreembodiments, the carbon content of the particles is less than about 3weight percent. In other embodiments, the oxidative sorbent compositionscontain activated carbon in an amount up to 30% by weight.

One or more embodiments of this invention pertain to a method for makingmineral sorbents for mercury capture comprising physical blending of thesorbent particles with a second particle component which is a flowmodifier, such as a powdered activated carbon, to effectively reduce theagglomeration of the mineral sorbent particles and significantlyincrease its mercury capture efficiency. The amount of second particlecomponent (i.e., flow modifier) added is such that it should reduce theagglomeration of the mineral sorbent particles and preferably not affectthe compatibility of the sorbent composition with cement for concreteapplications.

According to embodiments of the invention, the mineral substrateparticles comprise materials selected from the group consisting ofalumina, silica, titania, zirconia, iron oxides, zinc oxide, rare earthoxides, metal carbonate, metal sulfate, aluminosilicates, zeolites,clays such as kaolin, bentonite or attapulgite, heat-treated clays,chemical-surface modified clays, talc, fly ash, fluid cracking catalystparticles, dirt, and combinations thereof. When zeolites are used, aparticularly useful zeolite is 13X.

In one or more embodiments, the bromine species includes a salt selectedfrom the group consisting of sodium bromide, ammonium bromide, hydrogenbromide, potassium bromide, lithium bromide, magnesium bromide, calciumbromide, beryllium, zinc bromide, metal bromide and organic bromide thatcan release bromide or bromate ions and combinations thereof. Accordingto one or more embodiments, the particles have a bromine content in therange of about 0.1 weight percent and 20 weight percent. In otherembodiments, the oxidatively active halide is not limited to bromide,but includes iodide and chloride as well. By “oxidatively active” ismeant that the halide is a halide of a nonoxidative, alkaline metalcation, such as sodium, potassium, or alkaline earth metal cations, suchas calcium or magnesium. The halide can be also a halide of a transitionmetal cation such as zinc. While not wishing to be bound by a particulartheory, it is believed that when used in the oxidative sorbentcompositions of the present invention, the oxidatively active halideseither act as a surface for mercury to bind and become oxidized byoxygen in the fluid stream, or first themselves become oxidized byoxygen in the fluid stream, which can function to oxidize elementalmercury.

In a specific embodiment, the particles are selected from the groupconsisting of kaolin, FCC fines, and combinations thereof. In anotherspecific embodiment, the particles comprise as-mined kaolin without anybeneficiation. In another embodiment, the bromide salt is uniformlydispersed on the surface of the kaolin particles.

In one or more embodiments, a flow modifier is physically blended withthe brominated mineral sorbent to reduce agglomeration and improve flowcharacteristics of the mineral sorbents. The amount of the flowermodifier added is up to 30 wt % of the total blend. The flow modifiercan be a powder activated carbon or a halogenated activated carbon. Theflow modifier can be also mineral particles including particles ofheat-treated clay, surface-treated clay, silica, alumina, pseudoboehmite, FCC particles, and fly ash.

In a specific embodiment, the flow modifier is typically a materialwhich, when physically blended with the mineral sorbent substrate,produces a composition which improves the mass balance as compared tothe mineral sorbent substrate alone when measured by acoustically drivenaerosol injection methods such as described in more detail below. In oneembodiment of the invention the number of injections to obtain a massbalance of greater than or equal to those of activated carbon.

In another specific embodiment, the flow modifier is typically amaterial which, when physically blended with the mineral sorbentsubstrate, produces a composition which increases the overall mercurycapture rate by more than 10% as compared to mineral sorbent alone.

Another aspect pertains to a method of making brominated mineral sorbentfor the removal of mercury from a combustion gas in an exhaust gassystem comprising dispersing a bromide salt in a solid or liquid phaseonto mineral sorbent substrate particles, the mineral sorbent substrateparticles containing less than about 10 weight percent carbon. Incertain embodiments, the carbon content is less than about 3 weightpercent. Typically, the carbon is in the form of impurities, that is,carbon that has not been added to the sorbent. However, it is within thescope of the invention to add carbon, for example, by mixing the sorbentwith an organic bromide such as methyl bromide. The substrates and saltscan be those listed immediately above, according to one or moreembodiments. The method may further comprise drying the particles havingthe bromide salt dispersed thereon at a temperature in the range ofabout 25° C. and about 200° C. The bromide may have a loading level inthe range of about 0.1 to about 20 weight percent, and in specificembodiments, in the range of about of about 3 to about 15 weightpercent. The method may further comprise blending the brominated sorbentparticles with a flow modifier. The amount of the flow modifier is inthe amount of up to 30 wt % of the total blend.

Another aspect pertains to a method of blending cement with fly ash thatcontains the brominated mineral sorbents. The concentration of thebrominated mineral sorbent in fly ash is in the range of 0.01 to 20%.

The method may further include reducing the sorbent particle size to anaverage particle size of less than about 100 μm, and in specificembodiments, less than about 20 μm. In specific embodiments, the sorbentparticles comprise FCC fines, and the FCC fines comprise Y-zeolite in Naform. In one or more embodiments, the sorbent particles comprise mixtureof brominated kaolin and brominated FCC fines. In other embodiments, thesorbent particles comprise mixture of brominated fly ash and brominatedFCC fines. In other embodiments, the particles comprise mixture ofbrominated kaolin and one or more mineral substrate. In otherembodiments, the sorbent particles comprise mixture of brominated flyash and one or more mineral substrates. In other embodiments, theparticles comprise mixture of brominated FCC fines and one or moremineral substrates.

Another aspect pertains to a method of removing mercury from acombustion gas in an exhaust gas system comprising injecting a physicalblend of brominated sorbent particles and flow modifier particles, theblend particle system being adapted for removing mercury from acombustion gas in an exhaust gas system. The brominated sorbentparticles are selected from the group consisting of alumina, silica,titania, zirconia, iron oxides, zinc oxide, rare earth oxides, metalcarbonate, metal sulfate, aluminosilicates, zeolites, heat-treatedclays, chemical-surface modified clays, fly ash, fluid cracking catalystparticles, dirt, and combinations thereof. The flow modifiers areselected from the group consisting powdered activated carbon, brominatedpowdered activated carbon, heat-treated clay, chemical-treated clay,silica, alumina, pseudo boehmite, fly ash, and FCC particles. In certainembodiments, the sorbent particles comprise a spray-dried mixture ofzeolite and a bromine salt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing an ion-flight mercury capture profile of abrominated kaolin sorbent in a drop-tube reactor;

FIG. 2 is a comparative in-flight mercury profile of Br-PAC under thesame testing conditions as for the data in FIG. 1;

FIG. 3 is a graph showing the total mercury capture of a brominated 13Xzeolite sorbent at 2 second residence time with and without the additionof activated carbon at different injection rate; and

FIG. 4 is a graph showing the mass balance of brominated 13X zeolite andbrominated FCC fines compositions with and without blending of anactivated carbon flow modifier.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the invention, it isto be understood that the invention is not limited to the details ofconstruction or process steps set forth in the following description.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways.

As used in this specification and the appended claims, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly indicates otherwise. Thus, for example, reference to “a sorbent”includes a mixture of two or more sorbents, and the like.

Aspects of the invention provide improved sorbents, which may be used toremove mercury and other pollutants from the combustion gases, forexample, flue gases of coal-fired and oil-fired boilers, methods formanufacturing such sorbents, and systems and methods utilizing thesesorbents. The sorbents comprise brominated substrates in the form ofparticles having a carbon content of less than about 10 weight percent.A wide variety of substrates, regardless of their porosity, purity, orion exchange capacity, can be manufactured and used for mercury removalin accordance with the present invention. As used herein, the termsubstrate refers to the material onto which a bromide salt is dispersedand pollutant is then adsorbed in a pollution removal system.

Suitable substrate sorbent materials in accordance with embodiments ofthe present invention include any inorganic or organic materials thatare stable under the flue gas conditions (temperature, pressure, gascomponents, residence time, etc). The sorbents according to one or moreembodiments comprise particles having carbon content of less than about10 weight percent, and in specific embodiments, less than about 3 weightpercent. Suitable sorbents include, but are not limited to, commonlyused oxides such as alumina, silica, titania, zirconia, iron oxides,zinc oxide, rare earth oxides, metal carbonate, metal sulfate,aluminosilicates, zeolites, kaolin, metakaolin, fully calcined kaolin,talc, bentonite, attapulgite, talc, coal boiler fly ash, common dirt,fluid cracking catalyst (FCC) particles, etc.

In specific embodiments, especially useful particles comprise as-minedkaolin. As-mined kaolin refers to kaolin that has been mined and notbeneficiated or calcined. In another specific embodiment, especiallyuseful sorbent particles comprise fluid cracking catalyst particles. Inother specific embodiments, the sorbent particles comprise fly ashparticles. In addition to having favorable properties, these mineralsubstrates are also cost-effective and environmentally friendly.

Kaolin, also known as kaolinite or hydrous kaolin, is a common claymineral. Kaolin contains mainly silicon and aluminum in a layeredaluminosilicate structure. Kaolin is extensively used for coating,functional filler, ceramics additive and many other applications becauseof its fine particles size, white color, and inertness, among otherchemical and physical properties. Its low cost is also a key factor forits widespread use. Kaolin is also a very important raw material formany industries such as concrete, catalysis, and paper coating afterhigh temperature or chemical treatment. There are small amount ofimpurities in kaolin, depending on the location of the deposit. For manyapplications, the impurities in as-mined kaolin, such as TiO₂, Fe₂O₃,and organic materials or carbonaceous matter, need to be removed, whichis known as clay beneficiation. We found that, although kaolin has a lowBET surface area, typically 10-30 m²/g, it leads to a surprisingly highmercury capture performance when it is use as a low cost mineralsubstrate for our brominated sorbents. Furthermore, impurities inas-mined kaolin, such as the organic or carbonaceous materials, actuallyenhance the overall mercury capture efficiency of the brominated sorbentpossibly due to the increase of bonding of bromine species to thesubstrate and decrease of kaolin's density, stickiness, and wateradsorption.

Fly ash is the by-product of coal combustion. After experiencing hightemperature combustion in boiler, fly ahs has a bulk chemicalcomposition of aluminosilicate and other inorganic oxides such CaO, MgO,Fe₂O₃, and TiO₂, depending on the coal source and rank. PRB andsub-bituminous coals have high concentration of CaO in their fly ash.Under electron microscope, fly ash has a morphology of irregular beadsor broken beads. The surface area of fly ash is very low, BET surfacearea below 5 m²/g. It was found that residual unburnt carbon in fly ashcan increase the ionic mercury capture. We found that fly ashes,regardless of their coal sources, are all excellent low cost mineralsubstrate for our brominated sorbents.

FCC particles may be obtained from the end stage or intermediate stageof an FCC particle manufacturing process, or alternatively, they may begenerated during a fluid catalytic cracking process that uses FCCparticles and generates FCC fine particles. In particular embodiments,the methods and systems utilize fluid cracking catalyst fine particles,which will be interchangeably referred to as “FCC fines” or “FCC fineparticles”. The fluid cracking catalyst fine particles may be recoveredand separated from a fluid cracking catalyst manufacturing process orrecovered and separated from a fluid catalytic cracking process thatuses FCC particles and generates FCC fines. In specific embodiments,zeolite-containing FCC fines and intermediate FCC fines are provided assorbents for the removal of mercury from gas streams.

The terms “fluid cracking catalyst fines” or “FCC fines” are used hereinto refer to fine solid particles obtained from a fluid cracking catalystmanufacturing process, such as described in, but not limited to U.S.Pat. Nos. 6,656,347 and 6,673,235, and to particles generated andseparated during a fluid catalytic cracking process that uses FCCparticles. For particles formed during a fluid catalytic crackingparticles manufacturing process, the particles may be separated duringone or more intermediate stages of the manufacturing process, or at anend stage. A good fluid cracking catalyst requires the particle sizeabove 40 microns. During the production of these FCC catalysts, a largevolume of fine particles in the range of about 0 to 40 um in excess ofthat required for good fluidization in the refinery are often generated.Heretofore, a suitable use for these excess fine particles has not beenfound, and so they are therefore land-filled, which incurs cost for theplants. The disposal of the FCC waste by-products, referred as FCCfines, has been a long-standing concern for FCC manufacturing.

Depending on at which stage the FCC fines are collected, the maincomposition of the particles include zeolite (mostly Y-zeolite in sodiumform), kaolin, metakaolin, sodium silicates, silica, and alumina. Thus,the chemical and physical characteristics can be varied considerablybased on the FCC production process and post treatment. FCC fines have aBET surface area in the range between 200 to 600 m²/g. The surface areaof as-collected FCC fines can be further increased by washing. Heatingtreatment could also alter the surface area and surface chemicalproperties of FCC fines particles. Composition, porosity, and particlesize can all impact the mercury capture when FCC fines are used as amercury capture sorbent by itself or as the substrate for the brominatedsorbent. The most economical and readily available FCC fines are thosecollected during the production of Na—Y zeolite. The fines are collectedby a filter as a wet cake which can be then dried and ground orspray-dried. Thus, the use of FCC fines in manufacturing a mercuryremoval injection sorbent described herein not only provides aneconomical mineral substrate, but also helps solve the FCC wastedisposal issue. Furthermore, FCC fines alone have useful ionic mercurycapture capacity, as described in commonly-assigned United States PatentApplication Publication No. 2007/0289447 A1, dated Dec. 20, 2007, andentitled, Methods and Manufacturing Mercury Sorbents and RemovingMercury From a Gas Stream. Thus, when used as the substrate for thebrominated sorbent or physically blended with a brominated sorbent, FCCfines helps increase the mercury capture efficiency especially ionicmercury.

The sorbent particles according to one or more embodiments of theinvention comprise a single-component brominated material. According toother embodiments, the sorbent is a mixture of two or more brominatedmaterials, for example a mixture of brominated kaolin and brominated FCCfines. According to another embodiment, the sorbent comprises abrominated mixture of two or more substrates such as fly ash and FCCfines. Yet according to another embodiment, the sorbent is a mixture ofbrominated sorbent and a bromine-free substrate, for example a mixtureof brominated kaolin and FCC fines.

For a porous brominated sorbent, elemental mercury is oxidized intoionic form due to the bromide, and the ionic mercury is stored insidethe pores of the support. Pure zeolites have more cation-exchangeablesites, higher porosity, and thus higher mercury storage capacity thanFCC fines, kaolin, or fly ash, though the cost of a pure zolite isusually high. Most commonly used zeolites include aluminosilicatezeolites such A, X, Y, ZSM-5, Beta, chabazite, and titanosilicatezeolites such as ETS-10. Among all the brominated zeolites we havetested, those zeolites, such as 13X, which have the lowest Si/Al ratio,highest surface area and pore volume, and largest pore size gives thehighest mercury capture.

One of the major obstacles in using a mineral sorbent for capturingmercury in the flue gas is the agglomeration of sorbent particles. Thisis largely due to the strong interactions (stickiness) among mineralparticles as compared to, for example, a powdered activated carbon. Theagglomeration of sorbent particles greatly hinders sorbent flow abilityand its dispersion in the flue gas (i.e., the effective collision withthe mercury species in flue gas), and thus reduces its mercury captureefficiency. This invention shows that a physical blending of the sorbentparticles with a second particle component, such as a powdered activatedcarbon, can effectively reduce the agglomeration of the mineral sorbentparticles and significantly increase their mercury capture efficiency.The amount of second particle component (i.e., flow modifier) added issuch that it should reduce the agglomeration of the mineral sorbentparticles and preferably not affect compatibility of the sorbentcomposition with cement for concrete applications.

As used herein, the term “flow modifier” refers to any material thatreduces agglomeration of the particles of the mineral substrate of theinvention. Such flow modifiers are known in the art for reducing orpreventing clumping of solid particles such that they are “fluidized”and therefore tend to move as discrete particles which resemble a freeflow fluid rather than as chunks or agglomerated clumps. By reducing orpreventing agglomeration of solid particles by use of a flow modifier,processing and handling of such materials is simplified andmanufacturing processes are more consistent. Flow modifiers useful inthe invention may also be referred to as “powder flow modifiers,” “solidflow modifiers,” or “flowing agents.” A flow modifier useful in theinvention is typically a material which, when physically blended withthe mineral sorbent substrate, produces a composition which improves themass balance as compared to the mineral sorbent substrate alone whenmeasured by acoustically driven aerosol injection methods such asdescribed in more detail below. In one embodiment of the invention theblended sorbent composition obtains a mass balance greater than or equalto that of powdered activated carbon with 1-6 injections at 0% humidityas compared to a maximum achievable mass balance of about 40% or lessfor the mineral sorbent substrate alone. In further embodiments theblended sorbent composition obtains a mass balance greater than or equalto that of powdered activated carbon with 2-6 injections, 3-5 injectionsor 3-4 injections at 0% humidity. In specific embodiments, the blendedsorbent compositions obtain a mass balance of equal to or greater than70% after 1-6 injections or a mass balance of equal to or greater than80% after 3-5 injections at 0% humidity.

Loading

The substrate particles according to one or more embodiments arebrominated. In specific embodiments, bromide salts are dispersed onsubstrate. Non-limiting examples of the bromide salts include sodiumbromide, ammonium bromide, hydrogen bromide, potassium bromide, lithiumbromide, magnesium bromide, calcium bromide, beryllium bromide, zincbromide, other metal bromides, and organic bromides that can releasebromide or bromate ions and combinations thereof.

The loading level of bromide is up to about 50% by weight. In specificembodiments, the loading is in the range of about 0.1% by weight toabout 20% by weight. In a more specific embodiment, the bromine loadingis in the range of about 3% by weight to about 15% by weight.

The bromide salts can be dispersed on the surface of the sorbentparticles using any method so long as the bromide salt is well dispersedon the surface of the substrate. Some bromine species may get into thepores of the substrates such as Y-zeolite in FCC fines. Suitabledispersion methods include, but are not limited to, impregnation(incipient wetness), solid-state mixing, spray-drying, sprinkling ofsolution on the substrate, precipitation, and/or co-precipitation. If asolvent is required to disperse the bromide salt, it can be water or anorganic solvent. Non-limiting examples of organic solvents are acetoneand alcohol.

In a specific embodiment, the sorbent particles comprise about 0.1 toabout 10 weight % Br on kaolin or a fly ash. Kaolin and fly ashsubstrate particles require less bromide salt than other particles thathave been investigated to provide an effective sorbent. Also, it isbelieved that compared to other particles investigated, kaolin and flyash have less moisture sensitivity. Kaolin also has the desirableproperty that kaolin particles can be reduced to a smaller sorbentparticle size and it has a lower bulk density than fly ash. Although thepresent invention should not be not bound by any theory, it is believedthat the low surface area of kaolin and fly ash allows most of thebromide to be concentrated on the particle surface and thus have abetter chance to interact with mercury pollutant species during theshort residence time of the sorbent particles in the flue gas.

As noted above, the sorbent particles contain less than 10 weightpercent carbon, and in particular embodiments, less than 3 weightpercent carbon. Natural impurities in kaolin, such as intercalatedorganic or carbonaceous species, or the unburned carbon in fly ash mayhave a positive impact on the sorbent performance as the impurities canmodify the sorbent bulk density, surface hydrophobicity, and bondingstrength with bromine species.

Large scale sorbent production can be achieved by a spray-drying processwhich involves dissolving bromide salt in water first, adding mineralsubstrate to the solution, and then spray-drying the slurry in astandard industrial spray drier. In another embodiment, aqueous solutionof bromide salt can be added to a mineral substrate-water slurry beforespray drying.

Blending

The blending of the powdered halogenated mineral sorbent with a powderedflow modifier is done by a simple physical mixing. The mixing step canbe accomplished by adding the flow modifier particles continuously asthe spray dried sorbent particles exit from the spray drier. It can bealso achieved batch-wise by contacting the two particle types andstirring for a sufficient amount of time for mixing. The final blendedproduct should have a uniform composition and will have a grayishappearance if carbon is used as a flow modifier.

Without intending to limit the invention in any manner, the presentinvention will be more fully described by the following examples.

EXAMPLES Examples 1-15 Sorbent Preparation by Impregnation

The general procedures of making a brominated mineral sorbent accordingto one or more embodiments include (1) dissolving a bromide salt inwater; (2) impregnating the solution to the mineral substrate powderusing the standard incipient wetness method; and (3) drying the wetsolid either at room temperature by vacuum or at a temperature between100° C. and 200° C., and (4) grinding the dried solid to a particle sizebelow 325 mesh.

Table 1 lists the main ingredients of selected examples of brominatedmineral sorbents prepared based on the above procedures using differentmineral substrates.

TABLE 1 Selected Brominated Mineral Sorbent Preparations ExampleSubstrate W_(substrate) (g) Br Salt W_(Br Salt) (g) H₂O (g) 1 FCC fines23.0 NaBr 3.53 9.6 2 FCC fines 12.5 NH₄Br 1.56 7.2 3 CaCO₃ 10.5 NaBr1.76 2.5 4 (50% FCC 11.5 + 10.5 NaBr 3.5 12 fines + 50% CaCO3) 5 Fly ash20.0 NaBr 1.65 2.4 6 ATH 22.0 NaBr 1.65 13.7 7 Metamax 22.0 NaBr 1.6516.2 8 Kaolin-1 22.0 NaBr 1.65 7.7 9 Kaolin-2 22.0 NaBr 1.65 6.0 10Kaolin-3 22.0 NaBr 1.65 5.2 11 Kaolin-1 22.0 CaBr₂ 1.74 8.3 12 Kaolin-122.0 HBr 4.7 46 13 Kaolin-1 22.0 HBr 2.6 6.4 14 FCC fines — — — — 15Kaolin-1 — — — —

In table 1, three kaolin samples, -1, -2, and -3, were obtained fromBASF without further treatment. Kaolin-1 is an as-mined kaolincontaining about 2% naturally intercalated carbon. It has a grayishcolor. Kaolin-2 is another as-mined sample, containing less than 1%organic matter and having a beige color. Kaolin-3 is a beneficiatedsample from Kaolin-2. FCC fines particles were obtained by drying theFCC fines wet cake (obtained from BASF FCC manufacturing plants) at 105°C. overnight followed by grinding or by spray-drying the slurried wetcake in water. Fly ash was obtained from the baghouse of a power plant.Metamax is a BASF metakaolin product which was obtained by heattreatment of kaolin. ATH is an alumina trihydrate product from Chalco inChina. CaCO₃ (98%) was from Aldrich. HBr (48% aqueous solution), NaBr(99%), and NH₄Br (99%) were all from Alfa Aesar.

Examples 16-17 Sorbent Preparation by Spray Drying

To make the spray-dried samples, the general procedure comprisesdissolving bromide in water first, adding mineral substrate in thesolution and stir to make a uniform slurry that is suitable forspray-drying in a standard spray drier. Spray-drying outlet temperatureis 120° C.-160° C., typically 120° C. The spray drier outlet pressureand nozzles size are chosen in such that the final sorbent particle sizeis within the required range. Table 2 lists the main ingredients of twospray-dried samples made by two different spray driers.

TABLE 2 Selected Brominated Mineral Sorbent Preparations by spray dryingW_(substrate) W_(Br Salt) H₂O Spray- Example Substrate (kg) Br Salt (kg)(kg) drier 16 FCC fines 1.57 NaBr 0.153 3.35 #1 wet cake 17 Kaolin-1 159NaBr 11.8 409 #2 powder

Example 18 Mercury Capture Efficiency Measurement

The mercury capture efficiency was measured by an outside commercial lab(ICSET of Western Kentucky University) with a drop-tube in-flightreactor. The mercury capture efficiency (%) is defined by Equation 1.100×[Hg(inlet)−Hg(outlet)]/[Hg(inlet)]  (1)The total mercury is the sum of the ionic and atomic mercury species asillustrated in Equation 2.Hg_(total)=Hg⁰+Hg²⁺  (2)

The drop-tube reactor of ICSET was installed at a commercial powerplant. The carrier gas was the actual flue gas duct-piped from theboiler. The mercury in the actual flue gas has a distribution of about70% elemental mercury and 30% ionic mercury. The sorbent was injectedinto the reactor after being mixed with a fly ash in a ratio of 1:250.The fly ash served as a diluent to help inject the sorbent. The sorbentresidence time in the reactor is one second and the sorbent injectionrate is typically 4 lb/MMacf. The measurement was performed at about150° C. Table 3 lists the mercury capture efficiencies measured byICSET. For comparison, two reference materials are also listed: DarcoHg-LH from Norit and pure fly ash.

TABLE 3 ICSET Mercury Capture Efficiency Injection Capture rateEfficiency (%) Sample Sorbent Bromide lb/MMacf Hg_(Total) Hg⁰ ReferenceDarco Hg-LH — 4 55 64 Reference Darco Hg-LH — 8 78 85 Reference Pure flyash — 4 13 15 Example 1 12% Br/FCC NaBr 4 46 42 fines Example 2 12%Br/FCC NH₄Br 4 37 38 fines Example 3 12% Br/CaO₃f NaBr 4 52 49 Example 412% NaBr 4 44 48 Br/(CaCO3 + FCC fines) Example 5 6% Br/Fly ash NH₄Br 441 31 Example 6 6% Br/ATH NaBr 8 57 71 Example 7 6% Br/Metamax NaBr 8 6372 Example 8 6% Br/Kaolin-1 NnBr 4 52 54 Example 9 6% Br/Kaolin-2 NaBr 440 47 Example 10 6% Br/Kaolin-3 NaBr 4 35 46 Example 11 6% Br/Kaolin-1CaBr2 4 52 60 Example 12 6% Br/Kaolin-1 HBr 4 41 37 Example 13 11%Br/Kaolin-1 HBr 4 54 68 Example 14 FCC fines — 4 26 27 Example 15Kaolin-1 — 4 27 32 Example 16 12% Br/fly ash NaBr 4 41 47 Example 17 6%Br/kaolin-1 NaBr 4 69 66

FIG. 1 shows an in-flight mercury capture profile of a brominated kaolinsorbent in a drop-tube reactor. Note that the mercury concentrationdrops and recovers after the sorbent injection is started and stopped.FIG. 2 shows a comparative in-flight mercury profile of Norit DarcoHg-LH under the same testing conditions as for the data in FIG. 1. Thein-flight data shows that the brominated mineral sorbent has verysimilar mercury capture rate (drop slope) and capture efficiency (dropdepth) for both elemental mercury Hg(V0) and total mercury Hg(VT) as thecomparative carbon reference.

Example 19 Mercury Leachability and Cement Application

Mercury leachability is an important property for any injection sorbentdue to the environmental concern of their long-term stability afterexposure to the nature elements. The brominated mineral sorbentsdisclosed herein were tested for mercury leachability at IC SET usingthe standard Toxicity Characteristic Leaching Procedure (TCLP) method.The results showed that the mercury leachability of all the brominatedsorbents tested is well below the universal treatment standard value of25 ppb. The brominated mineral sorbents were also evaluated for theiruse, after mixing with fly ash, as additives in cement and concrete.Adding fly ash in cement reduces the overall usage of cement, which notonly reduces the cost but also finds value for fly ash, a wasteby-product of coal combustion. However, there are limits how much thefly ash can be added in the cement so that the properties of the finalconcrete properties will not be compromised. For example, ASTM C618requires that the amount of fly ash in concrete should be limited insuch that the water used in making concrete should be less than 105% ascompared to the control that is without fly ash, the strength activityindex (SAI) of concrete after 7 days should be higher than 75% of thecontrol, and the fineness (the particles retained on a 45 μm sieve)should be below 34% while the foam index (number of drops) should bestable and below 20-30.

Table 4 lists the concrete formulations and testing results usingcements that contain fly ash or fly ash plus a brominated kaolinsorbent. The data shows that adding 20% of fly ash to cement does notimpair the properties of cement and concrete in general. The data alsoshows that, after adding 5 and 10% by weight brominated kaolin sorbentin the fly ash, the concrete strength activity index is noticeablyincreased while other properties remain the same. It is clearlyindicated that the brominated mineral sorbents disclosed herein do notimpair the use of fly ash for cement and concrete application. On theother hand, in some cases, the presence of the brominated mineralsorbents actually enhances the properties of cement and concrete.

TABLE 4 Cement and Concrete Formulation and Testing Results Br/kaolinBr/kaolin Fly ash ~2 lbs ~4 lbs Control control injection injectionFormulation Cement 500 400 400 400 Sand 1375 1375 1375 1375 Fly Ash 0100 95 90 6% Br/kaolin 0 0 5 10 (Example 17) W/CM/Water .484/242 g.440/220 .460/230 .460/230 Water Requirement W/CM/Water .484/242 g.440/220 .460/230 .460/230 Water Requirement — 91 95 95 StrengthActivity 7 Day Compressive PSI 4500 3680 4010 4060 SAI — 82 89 90 CubeDensity g/cc 2.21 2.22 2.23 2.23 Fineness Retained on 45μ sieve % — 21.622.4 22.5 Passing 45μ sieve % — 78.4 77.6 77.5 (Fineness) Foam IndexTesting Number of Drops 5/5/5 9/10/9 9/9/9 10/9/9

Example 20 Blended Sorbent Preparation

In one embodiment, the general procedure for making the halogenatedmineral sorbent comprises dissolving the halogen salt in water first,adding mineral substrate in the solution, stirring to make a uniformslurry, and spray-drying the slurry to form the final sorbent particles.Typical spray drier outlet temperature is 120-160° C. The spray drieroutlet pressure and nozzles size or spinning wheel rate are chosen insuch that the final sorbent particle size is within the required range.

The second particle component, which serves as a powder flow modifier,is then physically added to and mixed well with the halogenated mineralsorbent particles. The blended powder mixture may then be packaged andshipped. In one example, a flow modifier is powdered activated carbon(PAC) in an amount of 10-20 wt % of the total blended product.

Brominated oxidative sorbent compositions were prepared by thespray-drying method described above. Briefly, bromide salt was firstdissolved in water, and 13X zeolite obtained from Sigma-Aldrich was thenadded to the solution while stirring. The total solid level in theslurry was about 30-40%. All the spray drying work was carried out in asmall Niro spray drier. The brominated 13X zeolite powder was physicallyblended with a commercial activated carbon obtained from Norit,Darco-Hg®, which contains no bromine.

Example 21 Apogee Field Testing

Mercury slipstream in-flight capture testing was conducted by ApogeeScientific, Inc. at a utility power plant burning PRB coals. Mercuryin-flight capture was conducted in a similar manner as those describedabove at ICSET except a pure sorbent powder was injected into the fluegas without using any fly ash diluent. Mercury concentration wasrecorded at 2 and 4 seconds of residence time at outlet ports andcompared to the inlet mercury concentration. The residence chambertemperature was maintained at 150° C. A 10% standard deviation with fourrepeating samples was reported by the testing facility.

The mercury capture efficiency (%) was defined by Equation 1 andEquation 2 as set forth above. The in-flight mercury capture wasmeasured with a drop-tube reactor. The carrier gas was the actual fluegas duct-piped from the boiler. The mercury species in the flue gas hasa distribution of about 70% elemental mercury and 30% ionic mercury.

Table 5 lists the in-flight capture test data for selected blendedpreparations of brominated 13X zeolite and Darco-Hg at 4 lb/Mmacfinjection rate. For nonblended sorbents with 10 and 7% Br loading(Samples 1 and 2), the total mercury capture, Hg(T), was about 65 and75% at 2 and 4 second residence time, respectively. Adding 10% Darco-Hgto 10% Br 13X zeolite or 20% Darco-Hg to 7% Br 13X zeolite (Samples 3and 4) actually caused a decrease of Hg(T). Surprisingly, adding 20% ofDarco-Hg in 10% Br 13X zeolite (Sample 5) resulted in a significantincrease of Hg(T) to about 86 and 82% at 2 and 4 seconds, respectively.

TABLE 5 Effect of Activated Carbon on the in-flight mercury capture ofSelected Brominated 13X Zeolite Preparations Total Mercury Capture, % Brin 13X PAC (Darco- Residence Residence Time Sample Zeolite, % Hg) inblend, % Time 2.0 sec 4.0 sec 1 10 0 64 76 2 7 0 65 75 3 10 10 60.0 65.04 7 20 60.3 60.3 5 10 20 86.0 82.0

FIG. 3 shows the total mercury capture of Samples 2 (without activatedcarbon) and 5 (with activated carbon) at 2 second residence time atdifferent injection rates. For unblended 7% Br 13X zeolite (Sample 2),the mercury capture expectedly increased as the sorbent injection ratewas increased from 2 to 4 lb/Mmacf. However, the mercury capture fellsharply at 8 lb/Mmacf possibly due to agglomeration of the sorbentparticles when the sorbent passed through the screw feeder. On the otherhand, the blend of 10% Br 13X zeolite and 20% Darco-Hg (Sample 5) showeda high total mercury capture up to 95% at 8 lbs injection rate. Overall,FIG. 3 shows that a blend of 20% of a flow modifier with halogenatedparticles of a mineral sorbent substrate can produce a sorbentcomposition which exhibits a total mercury capture of about 85% to 95%at injection rates of 4-8 lb/Mmacf. Thus, the activated carbon not onlycontributed to the overall mercury capture, but also served as a flowmodifier to help reduce the agglomeration of brominated 13X zeoliteparticles at high injection rate and enhance overall mercury capture.

With a larger spray drier, more brominated 13X zeolite samples wereprepared. The spray drier outlet temperature was maintained at 150° C. Atypical slurry for spray drying consisted of 100 lbs. NaBr, 1100 lbs. of13X zeolite and water. The brominated sorbent was then blended withdifferent activated carbons that were Br-free (obtained from JacobiCarbon and Norit, Samples 6 and 7). The samples were measured for theirmercury capture efficiency. Table 6 lists the mercury capture results bythe Apogee slipstream field measurement. Both blended samples (Sample 6ad Sample 7) contained 8.0 wt % Br in the brominated sorbent and 20 wt %of activated carbon of the total blend. The drop-tube slipstream reactorwas kept at 150° C. A pure brominated activated carbon (Sample 8), DarcoHg-LH from Norit, was used as a reference.

TABLE 6 Effect of different activated carbons in blended sorbents onin-flight mercury capture Total Mercury Capture % Residence Feed RateTime Residence Sample Carbon Source lb/MMacf 2.0 sec. Time 4.0 sec. 6aJacobi Carbon 1 77 87 (AquaSorb 500P) 6b Jacobi Carbon 2 89 94 (AquaSorb500P) 7 Norit (FGD) 2 92 96 8 (reference) Norit (Darco-Hg- 2 94 97 LH

Beside the Examples provided above on a blend of brominated (or otheroxidatively active halide) zeolite (or other mineral substrate particle)with a non-brominated activated carbon, blends of brominated activatedcarbon with a non-brominated zeolite or blends of brominated zeolite andbrominated activated carbon can also be used. Besides physicallyblending, the activated carbon and zeolite can first be blended,followed by bromination of the mixture. Furthermore, when using bromidesand 13X zeolite, another mineral substrate particle, such as FCC fines,may be blended in at any preferred ratio to reduce the cost of theoxidative sorbent preparation.

Example 22 Evaluation of Sorbent Preparation Methods

To evaluate the contribution of activated carbon per se to the overallmercury capture vs. its contribution by enhancement of the sorbentflowability, 20% PAC can be mixed with 13X zeolite and NaBr (10% Br),and then spray dried. The addition of 20% PAC to the mineral sorbent inthis manner is not expected to yield a higher mercury capture as docompositions in which the mineral sorbent is physically blended PACeither before or after halogenation. This experiment will demonstratethat when the advantageous flow characteristic properties of theactivated carbon are substantially compromised by the manufacturingmethod, its effectiveness as a flow modifier in the compositions of theinvention are also reduced with a corresponding reduction in the mercurycapture capabilities of the inventive compositions. That is, it is theflow enhancement obtained by physically blending PAC with the mineralsubstrate particles that yields the significant improvement in mercurycapture.

As used herein, the term “physically blended” and variations thereofrefer to a process or composition wherein discrete particles of themineral substrate component are mixed with discrete particles of theflow modifier component. Although there may be chemical speciesexchanged between the mineral sorbent and the flow modifier particles,such as a migration of some halogen anions from the mineral substrate tothe flow modifier particles, the physical blending does notsubstantially compromise the flow characteristics of the flow modifiercomponent. By physical blending, the flow modifier helps reduce theagglomeration and enhance the flow characteristic the mineral sorbentparticles. Halogenation may be performed on one or more of thecomponents prior to mixing or it may be performed on the mixture.

Example 24 Non-Carbon Flow Modifiers

To evaluate a non-activated carbon flow modifier, 20% graphite wasphysically blended to Sample 1 (Sample 7) and tested for mercurycapture. The graphite was purchased from Aldrich and has very littleporosity. Yet, the mercury capture of Sample 7 is much higher than thatof Sample 1, 74 and 79% at 2 and 4 second residence time and 4 lbs/Mmacfsorbent injection rate. This results demonstrated again that the mercurycapture performance of Sample 1, brominated zeolite, improved by a flowmodifier, whether the flow modifier has high porosity or not. Similarresults were obtained with other flow modifiers such as calcined claymicrospheres, surface treated clay produced by acid or organic coating,alumina, pseudo boehmite, silica, and their mixtures with activatedcarbon. Even with the low porosity of the graphite, performance wasimproved compared to mineral sorbent alone, although not as effective asactivated carbon. This result may be because the flow characteristics ofgraphite are not as good as activated carbon.

Example 25 Cement Foaming Index Measurement

The concrete compatibility of the blended sorbent compositions wasmeasured by the foaming index. This is a simple and preliminaryindicator of how an additive impacts the air entrainment admixture for acement. Ideally, after addition of any additive to cement, its foamingindex should not change significantly. More specifically, the number ofdrops of the air entrainment admixture required to produce a stable foamshould be below about 20-30. The control cement used in the foamingindex measurement is Cemex Type I Portland. The air entrainmentadmixture is BASF MB VR standard at 1:10 dilution, the fly ash is aClass C PRG combustion product. In a typical experiment, 1.0 wt % (whichis approximately equivalent to 4 lb/MMacf injection rate) of the sorbentwas physically blended with the fly ash and the mixture was then addedto the cement. For comparison, a pure activated carbon was alsophysically blended with the fly ash and then tested for its foamingindex. Table 7 shows that adding fly ash, fly ash plus Br/13X, or flyash plus Br/13X with up to 20% PAC blend yielded an acceptable foamingindex. The results demonstrate that the blended mercury capture sorbentof the present invention, exemplified by a Br/zeolite+flow modifier, iscompatible with concrete applications when the blend sorbent-latent flyash is used as a concrete additive. On the other hand, as shown in Table7, dramatic increases and an unacceptable level of foaming index wereobserved when the pure carbon (Norit Darco Hg-LH) was used instead ofthe mineral-based sorbent, which greatly limits the use of pureactivated carbon injection for mercury emission control from coal-firedflue gas.

TABLE 7 Effect of sorbent additive on cement foaming index # drops toproduce stable foam Sample Cement + Additive Test 1 Test 2 Test 3 11Cement control 4 3 3 12 Cement + fly ash 6 5 6 13 Cement + fly ash + 7%Br/13X 7 6 5 14 Cement + fly ash + 7% Br/13X + 9 9 9 20% Jacobi AquaSorb500P 15 Cement + fly ash + 10% Br/13X + 7 6 5 10% Jacobi AquaSorb 500P16 Cement + fly ash + 10% Br/13X + 10 10 11 20% Jacobi AquaSorb 500P 17Cement + fly ash + 10% Br/13X + 9 10 9 20% Norit FGD 18 Cement + flyash + Norit Darco 60 63 62 Hg-LH

Example 26 Mass Balance Measurement

To quantitatively measure the agglomeration of brominated mineralparticles and to evaluate how a physically blended flow modifier canreduce the agglomeration, a mass balance study was conducted by IllinoisInstitute of Technology using an acoustically driven aerosol injectionmethod. The experimental setup was described in detail elsewhere [E. M.Lee and H. L. Clack, Agglomeration and Triboelectric Charging, 2009EUEC]. Briefly, the experimental configuration features an acousticallydriven aerosol generation chamber designed to impulsively eject a presetmass of powder in the form of a particle-laden jet. Humidity in thechamber is maintained at 0%. An acoustic transducer is mounted to oneside of the chamber and is driven by an amplified signal controlled by afunction generator. Once the desired mass of powdered sorbent is addedto the chamber, the acoustic transducer sonicates the chamber and itscontents, simultaneously forming a particle suspension from the powderand impulsively ejecting the suspension through a small nozzle to form aparticle-laden jet. The ejected powder is captured in a HEPA filter andweighed after each test. The mass balance between the powder injectedinto and coming out of the aerosol generation chamber, and the number ofinjections required to reach an equilibrium value of mass balance can beused as a measurement of the degree of agglomeration of the powderparticles.

FIG. 4 shows the mass balance measurement results of several sorbentswith and without a PAC flow modifier.

As shown in FIG. 4, it took about 5 injections for an activated carbonreference (Darco-HG) to reach a mass balance of about 70%. Sample 1(Br/13X) never reached a mass balance above 40% even after 20 injection,a clear indication of a severe particle agglomeration. Adding 10% PAC inBr/13X (Sample 3) increased the mass balance slowly to above 80% afterabout 20 injections. Adding 20% PAC in Br/13X (Sample 5) dramaticallyreduced the number of injections to 3 to reach a mass balance of 80%.Substituting 13X zeolite with FCC fine particles also yielded a goodmass balance. The mass balance measurement data is consistent with themercury capture data in Table 5. It provides evidence that adding PAC inbrominated zeolite significantly reduce the agglomeration of sorbentparticles and increases its flowability.

Beside the Examples provided above on a blend of brominated (or otheroxidatively active halide) zeolite (or other mineral substrate particle)with a non-halogenated activated carbon, physical blends of halogenatedflow modifier with a non-halogenated mineral substrate or physicalblends of halogenated mineral substrate and halogenated flow modifiercan also be used. As an alternative to physically blending thecomponents after halogenation, the flow modifier and the mineralsubstrate can first be physically blended, followed by halogenation ofthe mixture. Furthermore, when using bromides and a zeolite such as 13X,another mineral substrate particle, such as FCC fines, may be blended inat any preferred ratio to reduce the cost of the oxidative sorbentpreparation.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit or scope of the invention. Forexample, while the sorbents disclosed herein are particularly useful forremoval of mercury from the flue gas of coal-fired boilers, the sorbentscan be used to remove heavy metals such as mercury from other gasstreams, including the flue gas of municipal waste combustors, medicalwaste incinerators, and other Hg-emission sources. Thus, it is intendedthat the present invention cover modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalents.

What is claimed is:
 1. A sorbent composition for removal of mercury froma flue gas, the sorbent composition comprising one or more bromides of anonoxidative metal, spray-dried with one or more mineral substrateparticles, and a flow modifier physically blended with the spray-driedmineral substrate particles in an amount sufficient to reduceagglomeration of the mineral substrate particles when injected into theflue gas, wherein the bromides of the nonoxidative metal are dispersedon the spray-dried particles to provide spray-dried brominated sorbentparticles blended with the flow modifier for injection into the flue gascontaining mercury, wherein the nonoxidative metal is selected from thegroup consisting of sodium, potassium, calcium, magnesium, andcombinations thereof, wherein the flow modifier is present in an amountof up to 30% by weight.
 2. The sorbent composition of claim 1, whereinthe mineral substrate particles are selected from the group consistingof alumina, silica, titania, zirconia, iron oxides, zinc oxide, rareearth oxides, metal carbonate, metal sulfate, aluminosilicates,zeolites, clays, heat-treated clays, chemical-surface modified clays,talc, fly ash, fluid cracking catalyst (FCC) particles, dirt, andcombinations thereof.
 3. The sorbent composition of claim 2, wherein themineral substrate particles are selected from the group consisting ofzeolite, FCC particles, fly ash, clay, and combinations thereof.
 4. Thesorbent composition of claim 3, wherein the zeolite is 13X.
 5. Thesorbent composition of claim 4 which comprises brominated 13X zeolite,FCC particles, clay and activated carbon.
 6. The sorbent composition ofclaim 1, wherein the composition exhibits a capture of about 85-95%mercury at a residence time of 2-4 seconds, an injection rate of 4-8lb/Mmacf, and a flue gas temperature of 150° C.
 7. The sorbentcomposition of claim 1 which exhibits a mass balance as measured by anacoustically driven aerosol injection method of equal to or greater than70% after 1-6 injections at 0% humidity.
 8. The sorbent composition ofclaim 7, wherein the flow modifier comprises activated carbon present ina range of 10-20% by weight.
 9. The sorbent composition of claim 1,wherein the flow modifier is present in amount from about 10% to about30% by weight and the mineral substrate particles are selected from thegroup consisting of kaolin, heated treated kaolin, chemical-surfacemodified kaolin, and combinations thereof.
 10. The sorbent compositionof claim 9, wherein bromide of the nonoxidative metal is NaBr.
 11. Amethod for removing mercury from a flue gas stream, comprisingcontacting the flue gas stream with the sorbent composition of claim 1.12. A method for removing mercury from a flue gas stream, comprisingcontacting the flue gas stream with the sorbent composition of claim 9.13. A process for preparing the sorbent composition of claim 1comprising dispersing the one or more bromides of a nonoxidative metalon the spray-dried particles and physically blending the brominatedspray-dried particles with up to 30% by weight of the flow modifier. 14.The process of claim 13, wherein the flow modifier is brominated priorto blending with the spray-dried mineral substrate particles.
 15. Theprocess of claim 13, wherein the bromide of the nonoxidative metal isNaBr, the mineral substrate particles comprise 13X zeolite, and the flowmodifier is activated carbon present in an amount of about 20% byweight.
 16. The process of claim 15, wherein the zeolite comprises about10% Br by weight.
 17. A sorbent composition for removal of mercury froma flue gas, the sorbent composition comprising one or more bromides of anonoxidative metal, dried mineral substrate particles, and a flowmodifier physically blended with the mineral substrate particles in anamount sufficient to reduce agglomeration of the mineral substrateparticles when injected into the flue gas, wherein the bromides of thenonoxidative metal are dispersed on the dried particles to provide driedbrominated sorbent particles blended with the flow modifier forinjection into the flue gas containing mercury, wherein the compositioncomprises about 10% by weight of bromine loaded on 13X zeolite and thebromide of nonoxidative metal is selected from NaBr and wherein the flowmodifier is activated carbon present in an amount of about 10-20% byweight.
 18. A method for removing mercury from a flue gas stream,comprising contacting the flue gas stream with the sorbent compositionof claim 17.